The invention relates to a fabric for the sheet forming section of a papermaking machine which is made up of a double layer fabric with an upper and lower layer of transverse threads interwoven with longitudinal threads. The transverse threads of the upper layer and the longitudinal threads form crimps oriented towards the paper side with their highest points disposed in the plane of the paper. Within each weave repeat the longitudinal threads are interwoven two times into the upper layer of transverse threads, and the number of transverse threads in the upper layer is twice as high as in the lower layer.
Such double layer sheet forming fabrics are disclosed in German Auslegescrhrifts Nos. 2,263,476; 2,540,490; and 2,706,235, and in European Patent Publication No. 30,490. In the fabric shown in FIG. 2F of German Auslegeschrift No. 2,706,235, the density of transverse threads in the upper layer is likewise twice as high as in the lower layer. Although such sheet forming wires exhibit better marking characteristics than single layer sheet forming wires, they are nevertheless unsuited for the production of paper of the type extremely sensitive to marking.
According to German Auslegeschrift No. 2,706,235, the marking characteristics are improved by extremely long weft floatings, i.e., transverse thread floatings. European Patent Publication No. 30,490, and U.S. Pat. No. 4,333,502, attempt to reach the same goal with long warp floatings.